1. Field of Art
The present invention relates to an automatic conveyor system, particularly of the reciprocating walking beam accumulating type.
2. Description of Prior Art
Representative systems for conveying loads in walking beam type conveyors are illustrated by U.S. Pat. Nos. 3,369,650, 3,500,992 and 3,552,543. In these patents a transfer bar (viz. slide 18 U.S. Pat. No. 3,552,543 ) performs a separate step or movement to determine whether the carriers should be elevated to their feed positions to lift the workpieces from their respective work stations. For example, both U.S. Pat. Nos. -992 and -543 begin their lifting sequence in an initiating position to the left (or upstream) of the position where the carriers will assume their feed positions. The transfer bar is then shifted to the right (or downstream) to determine which carriers will be elevated to their feed positions until the transfer bar reaches a certain position, whereupon the transfer bar is elevated for lifting the workpieces from their work stations. Accordingly, when the transfer bar is returning to its initiating position, it again passes its feed position and is located initially to the left thereof.
The extra step involved for determining which carriers are to be elevated is extremely inefficient. If the decision which carriers are to be elevated is determined just prior to carrier engagement with the workpiece, i.e., at the last possible moment the decision could be made, a greater amount of conveyor time could be used by the operators for placing or removing workpieces onto or from the conveyor without causing a malfunction. Morever, if a conveyor could make the feed position decision at the last possible moment, conveyor time would be considerably saved, since the extra step for determining feed positions would be eliminated. In addition, using the construction of U.S. Pat. Nos. -992 and -543, if a workpiece was placed on the conveyor after the carriers have assumed their feed positions or during the decision process, the conveyor could malfunction creating increased maintenance cost and lack of reliability, as well as substantial inflexibility.